Royal Newfoundland Constabulary Chief Bill Janes says a male suspect was arrested Thursday night not far from the soccer pitch in the community near St. John's.
He could not confirm the age of the victim who was playing in an event, nor confirm the age of the suspect or whether he and the victim knew each other.
No charges had been laid as of late Thursday.
Janes said the stabbing happened at about 7:50 p.m. local time as horrified parents looked on.
The extent of the victim's injuries was not clear late Thursday.
The Conception Bay South Soccer Association posted a statement on its website saying it is ”shocked and saddened” by the incident at Topsail Field.
It said crisis intervention counsellors will be available for anyone who needs assistance over the next few days.
The association also said all activities at Topsail Field and Clubhouse are suspended until further notice.